Significant clinical-imaging MRI systems manufacturers that I can think of
off-hand include Siemens (Munich), Philips (Eindhoven/Best), GE Medical
Systems (New Berlin/Waukesha, WI), Picker (Highland Heights, OH), Toshiba
(Nasu, JA), Elscint (Israel) ... I'd guess that these guys probably account
for 90-95+% of all 1.0T and larger MRIs world-wide.
I'd guess that the vast majority of "pulls" are pulled while operating
normally but at the low edge of gain/output/linearity specs, but a few
undoubtedly fail before being pulled.
Caveats emptor: 1) DON'T buy ANY 8877 code-dated between roughly 8626 and
8826 - the approximate period of the "all new 8877's are likely to fail
between 200 and 3000 hours" debacle. 2) I wouldn't buy any "pulled" 8877,
3CPX5000A7 version, or any other tube without a firm money back guarantee
allowing enough time to test it.
73, Dick
73, Dick
-----Original Message-----
From: Dave Kirkby [SMTP:davek@medphys.ucl.ac.uk]
Sent: Friday, May 29, 1998 5:30 AM
To: W9JA Paul Hellenberg
Cc: amps
Subject: [AMPS] Re:
W9JA Paul Hellenberg wrote:
> I have been told by more than one person that 8877s are used in some
> type
> of hospital equitment (CAT or MRI) and that these are changed out from
> time
> to time based on number of hours used. Does anyone know anymore about
> this.
> For example what type of hospital equipment, are the tubes still worth
>
> using after pulled, etc? Please respond to me directly.
>
I dont know for sure, but suspect the most likely candidates are
magnetic resonance imaging (MRI), or to give its its old name, nuclear
magnetic resonance (NMR) - the latter being dropped, as the word
'nuclear' alarms people. As for makes, I dont know many, but Seimens and
GE are two I can think of.. I would add that the NMR systems we have
where I work, all have semiconductor power amps, with *peak* powers of
about 1 kW. Average powers are *much* lower. Quite why such large tubes
are used I dont really know, but I know they are indeed used. I'll ask
around - we have several experts on MRI around here. Perhaps its just a
case of very conservative rating.
I bought a couple of YC156's (pulsed 5kW tubes) with 'GE Medical
Systems' stamped on them.
My guess is that any medical tubes would probably have different type
numbers on them, to prevent technicians in hospitals replacing them. The
manufacturers of the equipment would probably want to avoid this
possibility, so the numbers on the tubes might be Y, or YC, rather than
the more common 3CX, 3CPX etc. This would leave you with the problem of
getting data, as I dont think either Eimac, or the medical equipment
manufactuer, would wish to disclose this.
I would have thought any pull would be pulled quite early - its not the
sort of application where failures are wanted.
Dave Kirkby (G8WRB),
Dept of Medical Physics,
University College London.
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